Spark plug



INVENTORS IE H.

ENRY

MM 1, Eli

S PARK PLUG Filed Oct. 7, 1942 L H. MIDDLETON ETAL.

3-3115! liiilllii a L MJDDLE TON STQLTENBERG ATTORNEYS Lss Y 11H W EE =2 5 m SHHI March 2, 1948.v

Patented Mar. 2, 1948 PATENT OFFICE SPARK PLUG Leslie H. Middleton and Delbert Henry Stoltenberz, Toledo, Ohio Application October 7, 1942, Serial No. 461,196

3 Claims. (01. 123-189) This invention relates to spark plugs, more particularly to methods of positioning center electrodes in ceramic insulators for forming a seal therebetween.

The problem of holding and sealing a center electrode in the bore of a ceramic insulator core has generally involved the use of a shouldered bore in the insulator against which a shoulder on th center electrode rested with sealing material, either in the form of compacted powder or fused glass positioned above the shoulder on the electrode. Due to the refractory nature of the material of which the insulator is composed, it is dimcult and impracticable to accurately position the shoulder in the bore after firing the ceramic insulator, and uneven shrinkage during firing causes wide variations in the longitudinal placement of the shoulder it formed before firing. This variation gives rise to manufacturing diificulties which are aggravated by the fact that the shoulder during firing often loses its sharpness and clear definition.

The present invention obviates these difiiculties by providing a smooth bore in the insulator having substantially a uniform cross section into which a center electrode is inserted and held in a predetermined position with reference to the exterior of the insulator by locating from its external shoulder in the preferred embodiment. A novel holding means is provided to hold the center electrode in this predetermined position during the period in which a holding and sealing body of compacted granular material such as powdered talc or a mixture of powdered talc and comminuted metal, is packed into a space between the center electrode and the bore of the insulator. By establishing a predetermined relation between the external shoulder of the insulator and the firing tip of the center electrode, the spatial relation of the electrodes of the completely assembled spark plug may be easily controlled, thereby obviating final trimming of the firing tip of the center electrode, which if it is made of refractory material such as tungsten often presents diflicult and expensive production problems.

The use of a smooth bore in the insulator simplifies the manufacture of the insulator and at the same time gives a stronger insulator. Its use also facilitates the assembling operations of the spark plug by giving more accurate control of the .parts so that a smaller number of rejections is made possible.

1 It is therefore a principal object of this inven- 'tion to provide an insulator for a spark plug hav- 2 ing a smooth bore of substantially uniform cross section into which a center electrode is positioned by a body of compacted powder.

It is a further object of this invention to provide a method of positioning a center electrode in a smooth bore of an insulator, wherein the insulator and the electrode are held externally in a predetermined relation during the compacting of a body of powder between the bore and the electrode to form a holding and sealing body.

It is a further object of this invention to position a center electrode in a smooth uniform bore of a ceramic insulator by a method wherein one end of the electrode is held in fixed, predetermined position with reference to the external shoulder of the insulator during the period in which a compacted body of powder is packed in position between the electrode and the bore of the insulator to form a holding and sealing body.

It is a further object of this invention to provide a method of sealing a center electrode in a ceramic insulator of a spark plug by a holding and sealing body of compacted granular material, packed between the electrode and uniform bore in the insulator.

Other objects and advantages of this invention relating to the arrangement, operation and function of the related elements of the structure, to various details of construction, to combinations of parts and to economies of manufacture, will be apparent to those skilled in the art upon consideration of the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

Fig. 1 is an elevational view partly in section showing a jig utilizing the method of holding an insulator and electrode in predetermined relation during the period in which granular material is compacted in position.

Fig. 2 is a sectional elevation of an unshielded spark plug to which the invention has been applied.

Fig. 3 is a sectional elevation of a shielded spark plug to which the invention has been applied, and

Figs. 4 and 5 are sectional elevations of insulators and holding jigs illustrating modifications of the invention.

Referring to the drawings particularly to Fig. 1, a ceramic insulator in is provided which is constituted of a highly refractory insulating ma-- terial such as sintered corundum or the like, hav ing a longitudinal bore II which is smooth and "on the lower end of the aesmos An internal shoulder ll is provided on the interior of the shell E5 to cooperate with the lower external shoulder ill on the insulator to form a seat. A gasket id of 'rela'- tively soft metal is positioned between the shoulders to form a leak-prodf joint'wh'en the" On the upper end of the shell l5, a lip '19 is provided which is plug is completely assembled.

adapted to be turned in to form a holding portion to cooperate with the upper external shouldor 13 of the insulator to form a one-piece plug. In Fig. 2 on the right side of the drawing the lip is shown in its original form before being turned in as shown at |9a at-the left side. A gasket Ed is provided to seat the in'tu'rned lip i961, on the shoulder 13. After the shoulder I9a. is turned in, the plug may be given "a 'hot press, where the application of heat and pressure to the shell (shown schematically 'in Fig. 2), a portion between the lip l'saa'n'dtheshoulder I? is thermoplastically collapsed to form a leak-proof joint at the gasket l8. This process is well-known in the 'art and need not be described in further "detail.

As has already been described, the central longitudinal bore 'I'l of the insulator is uniform in cross section'which'allows the use of a cylindrical center electrode 21, preferably formed of ametal having 'a coefficient of expansion matched to the coeiiicient of expansion of the insulator. For example if the insulator is made of aluminum f'oxide, the center wire or electrode may conveniently be made of nickel-iron alloy. To give the firing tip of the electrode, resistance to spark erosion, a piece of tungsten 2IA may be welded inpla'ce'adjac'ent the lower "end of the insulator to provide a projecting "tip to cooperate with a fixed electrode 22 (shown in Fig. 2) which may be conveniently brazed inposition on a shoulder 23 threaded portion of the shell.

Inasmuch as the bore H in the insulator is smooth and the center-electrode 28 is cylindrical,

a separate mjeansis provided to hold the two parts in a predetermined rel'ation'while a sealing and holding body 24, "comprising a compacted body of granularmaterial, is packed into position in a space 25'fo'rme'd between Ta reduced portion 2m ofthe center electrode 'a'nd'the bore ii. A shoulder 26 is formed on the electrode 2i at the point where the re'duced'portion joins with the "cylindrical portion which substantially fllis the lower portion of the bore. The shoulder 23 forms an abutment against which'the granulated material may be pa'cked'asshown in Fig. 1. Prior to the positioning of the holding and sealing body 2 in the space 25 cement is preferably positioned "between the cylindrical portion of the electrode and the lower portion of the bore, although it is generally desirable to avoid the use of'cement in the space 25' where the "cement would interfere with the packing of the granular material.

In Fig. 1, a packing press 'or'jig is illustrated which holds the "center electrode 2! between a 'diiced portion 26a of the center electrode. spring pressed mandrel 3B is adapted to slide versocket 27 in a base member 28 whose depth is made adjustable by lock screw 29 and a spring pressed mandrel 3! positioned in a verticallymovable head 3i. The head is movable through the agency of a rack and gear arrangement actuated by a manually operable lever 32, which rotates a gear 33 journaled in an upright 34 to cooperate with a rack 35 on the. head 3|. On the lower end of the head 3i, a hollow ram 36 is provided havingan external diameter slightly smaller than the bore H of the insulator it, and an internal diameter slightly larger than the re- The tically inside or the ram and is provided On its lower end with a reduced portion 30a which 00- operates with 'aver'tical bore 2!!) in the reduced portionZla of the center electrode, so that the spring urging the mandrel downwardly will be enabled to hold the bottom tip of the center electrode iii in the soketZl of the base member.

The'base member 2 8is provided with a boss 28!: concentric with the socket 21, having a series or bores t l, 38, and 39 all concentric with the soclset El, and adapted to closely fit the 'exterior of the spark plug insulator lit to hold the same firmly in upright position. The shoulder Eta iorme'd between the bores 38 "and 39 is given the same contour as the 'lower shoulder i l on the insulator id and forms a means of locating whereby the relation between theshoulde'r hi and the lower tip end -2lA of the center electrode is predetermined. This relation 'is adjustable through the action of the lock screw -2' which determines'the depth of the socket 21. Anyother exterior point on the insulator may be used as-alocating point, as for example in Figs. 4 and 5, the tip of the insulator is used as the determining point. Other points will readily suggest themselves to those skilled in the art. The exterior'shoulder M if the'insulator is preferable as a locating point inasmuch as the dimensions of the shell are largely determined by theposition of the internal shoulder H, which will give better m-atcli'ing of the electrodes when the plug is completely assembled.

Withthe exact -controlof the tip prdje'ction, made possible by the use of-deviee disclosed Fig.1, the relation of the electrodesat the-firin tip can'b'e pred'etermined'sc asto obviate undesired projection or thetung'ste'n tip below the fixed electrode. I f"aprojectionof this kind occurs, it must beground oiisp'ec-ial methods inasmuch as tungsten is a very refractory material. These extra "operations'i-ncur greater ea pause and even complete rejection of the as sembled plug. 7

If desired a v rtical fiutingdllmay be provided on the center electrode, preferably adjacent *the lower end thereof which providesa convenient method of centering the cent-er electrode'in the insulator bore. This-method has the add'eda'dxvantage of allowing "cement positioned between the center electrode and the bored; becomemore evenly distributed, which is essential to give "a series of fabricated plugs more uniform heat ranges. V

In order to position-acenter'el-ectrodein the bore of an insulator, the bore is first covered with a coating of cement which may beaccomplished conveniently by completely filling the bore with'cement. A swabis then temporarily attached to the upper end of the "electrode and pushed through "the bore fromfthe firin ftip, removing all "but "athin layer of cement from the bore. This removes the superfluous cement from the bore and yet leaves a relatively thin, uniformly distributed coating of cement between the bore and the larger portion of the electrode. The swab is then removed from the upper end of the electrode and a small perforated washer 4| either of rubber or asbestos or like material is positioned on the reduced portion of the electrode and pushed downwardly thereon until it rests on the shoulder 26 as shown in Figs. 1 and 2. This downward thrust of the washer 4! causes the perimeter of the washer to contact the wall of the bore II and by a squeegee efiect moves substantially all the cement downwardly before it as it moves against the shoulder. The upper portion of the bore adjacent the reduced portion 2Ia of the electrode is thereafter substantially dry and free of cement so as not to interfere with the packing of granulated material such as powdered talc in the space 25.

The cement used for this purpose is preferably a cement which sets by a chemical reaction, rather than a cement which sets after the solvent evaporates, however such a cement may also be used if desired.

While the cement is still moist and unset the cemented assembly of the center electrode and insulator is positioned in the holder portion of the packing device shown in Fig. 1. The tip portion 2th of the center electrode is positioned in socket El and forced downwardly against the look screw 29 and the external shoulder 14 of the insulator is thrust into contact with the shoulder 39a on the holder device to establish a fixed relation between the positions of the bottom tip ZIA of the center electrode and the external shoulder M of the insulator. A small funnel member 42 preferably of magnetic material is positioned on the top of the insulator as shown in Fig. 1 by embracing a portion thereof to hold the funnel member firmly in position. The spring-pressed mandrel 30 is then brought into engagement with the upper end of the electrode by putting the tip 30a into the bore Zlb of the electrode. This firmly urges the lower end or tip ElA against the lock screw 29.

With the parts in the position shown substantially in Fig. l, powdered or comminuted material in granular form is poured into the funnel member 42 by any convenient means such as a cup 420. so that it falls by gravity into the space 25 in the vertically positioned insulator 10. An operator then actuates the handle 32 in a manner to advance the ram 36 downwardly into the space 25, where it contacts the loose powdered material and compacts it into position against the shoulder 26 on the electrode 2|. After the first portion of the powdered material is compacted in position the ram 36 is again raised to above the funnel member 42 to allow a new portion of loose powder to fall into the space 25, whereupon this loose portion is compacted by lowering of the ram, and so forth until the necessary amount of powder has been compacted in position in the space 25 to form a holding and sealing body between the electrode and the bore of the insulator. An alternating current solenoid 43 may be conveniently positioned adjacent the funnel member 42 which may be of magnetic material, and provided with a spring member 44 to cause the funnel to be agitated to the desired degree so that the loose powder will readily fall into the space 25 when the ram 35 is in raised position. This agitation facilitates packing and reduces the time required to accomplish the positioning of the compacted body.

The assembly is then removed from the holding device shown in Fig. 1, and the upper end of the compacted body is reamed out to a predetermined distance from the top of the insulator, a shouldered reamer being a convenient means to accomplish this purpose. A terminal tip 45 as shown in Fig. 2 is placed on the top of the electrode, having a depending flange 45a cooperating with the space 25, and the upper end of the electrode is peened to open the bore Zlb to hold the tip 45 permanently in position. The com-= pleted assembly is then positioned in the shell [5 and the plug completed in the well known manner.

In Fig. 3 an aviation spark plug of the shielded type is shown to which the invention has been applied. This plug is of two-piece construction, having a lower shell portion 46 adapted to be attached to the cylinder of an internal combustion engine by a threaded portion 41, and having an upper sleeve portion 48 threadedly-attachod to the shell portion 46. An insulator 49 is positioned between internal shoulder 50 in the shell portion and the lower end 48a of the sleeve portion, being provided with an intervening spring member 5! to give resiliency to theassembly. The sleeve portion is provided with a tubular insulator 52 as is well known in the art.

The insulator 49 is again provided with v a smooth longitudinal bore I I of uniform cross section in which again an electrode 2| is positioned vas described before with reference to Figs. 1 and 2. The construction shown in Fig. 3 is substan tially the same as that shown in Fig. 2 and is made by the same methods and will not be described again in detail. A fiat terminal tip 53 is provided to facilitate connection, the tip being attached in a similar manner as described with reference to Fig. 2-.

. h ai of c nst c n o h a ion spark plug disclosed in Fig. 3, particularly with reference to the resilient member 51, are further disclosed and claimed in a copending application Serial No. 482,688, filed April 12, 1943, by Chester Cipriani and Carl Eaton, the application being assigned to the same asslgnee, and now having matured into Patent No. 2,389,597, granted Nov. 27, 1945.

In Fig. 4 a modification of the invention is illustrated in which a cylindrical center electrode 55 is used in a smooth bore 58 in an insulator 51, the electrode being somewhat smaller than the bore to provide an annular space 58 between the parts into which is compacted a body 59 of granular material. The electrode 55 is again held between a socket 60 in a holding member BI, and a spring-pressed mandrel 62 as described in reference to Fig. 1, and the body 59 of compacted material again positioned in the bore as described before. A vertical fin 63 is provided above the socket 60 to embrace the tip of the electrode 55 and to fill the bottom end of the bore, to provide an abutment 64 against which the powder is compacted in position to form the body 59. When the body 59 is compacted in position the fin 63 will provide an annular vacant space into which a cement or readily fusible glass may be positioned to protect the compacted body from the hot gases in the cylinder of the engine. The locating position to determine the relation between the center electrode and the insulator may in this instance be the firing tip of the insulator.

I-nFigZ 5 a slight modification-(twig. p enom in which the fin 6 3 is dispensed; with and the powder is compacted in the lower portion of the insulator bore directly againstthe holding means flu}. Otherwise the modifications shown in Figs. 4 and 5 are substantially thesarnea It is to be understood that "the above detailed description of the present invention is intended 'to disclose an embodiment thereof to those skilled in the art, but that 'the invention is not 10 to be construed as limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of hem-g practiced and carried out in various ways without departing from the spirit of the invention. The language used in the specification relating to the operation and function of theelement-s of the invention is employed for purposes of description and not of limitation, and it is not intended to'limit the-scope of the following claims beyond the requirements of the prior art.-

What is claimed:

1. In aspark' plug, an insulator with a smooth uniform longitudinal bore of substantially uniiorm diameter, anelectrodein the bore, a shoulder on the electrode between a larger portion of the electrode substantially filling the bore ad- 'jac'en't the lower end of the b'ore, and a-smaller portion of the electrode adjacent the upperend of the bore, and a body of compacted granular material packed against the shoulderin the space between the bore of the insulator and-the smaller end of the electrode to form a holding and seal- 'ing body'between the electrode arid't'he insulator.

'2. In a spark plug, an insulator with a longitudinal bore of uniform cross-section throughout its length, a cylindrical electrode positioned in the bore substantially filling the bore adjacent the firing end of the insulator, a shoulder on the electrode adjacent the outerend of the insulator formed by a concentric portion "of the electrode of smaller cross section than the larger portionwhereby a space is formed between the bore and the smaller portion of the electrode, and a body of compacted granular material positioned against the shoulder in the space between "the smaller portion of the'electrodeand the bore to form a holding and sealing body betweenthe electrode and the insulator. V

3. In a spark plug; an insulator wlth'a longitudinal bore of uniform cross sectionand external shoulders adapted tocooperate with an embracing metallic shell, a cylindrical electrode positioned in the bore substantially filling the bore and extendingbeyond the insulator to a predetermined position with reference to the external shoulders, a shoulder on the electrode ad- J'acent theouter end of the insulator formed 'between the lower larger portion of the electrode and a smaller portion of less cross-sectional area than the bore to form a space between the electrode and the bore, and a body of compacted material positioned against the shoulder-in the space between the smaller portion of the electrode and the bore to form a holding and sealing body between the electrode and the insulator.

LESLIE H. MIDDLETON. D. HENRY STOLTENBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,371,924 Moore Mar. 15, 1921 1,968,314 Rohde July 31, 1934 1,999,785 Ro'hde Apr. 30, 1935 2,020,966 Rohde Nov. 12, 1935 2,020, 67 Rohde Nov. 12, 1935 2,254,082 Meyer Aug. 26, 1941 2,367,445 Stoltenberg Jan. 16, 1945 

